Bacteria

Collier's New Encyclopedia (1921)

organisms that comprise a class of low plants, the importance of which is due to their power of producing profound changes in life. The terms bacteria, germs, microbes, bacilli, are popularly used to denote these microscopic objects. Bacillus means a little rod. The term is properly applicable to only such microbes as are rod-shaped. The word microbe (from the Greek, mikros, small, and bios, life) is a term which was coined to include all of the microscopic plants commonly included under the terms bacteria and yeasts. Plants or Animals. --Bacteria possess characteristics of plants and animals. They resemble animals in their common power, independent motion, and in their habit of living upon complex bodies for food. But in general form, methods of growth, and formation of threads and spores they resemble plants. Though there are hundreds of different species there are only three general formsspheres, rods, and spirals, reminding of billiard balls, pencils, and corkscrews. There is some, though slight, variation in size. All are extermely minute and never visible to the naked eye. They range in size from 1-100000th to 1-3000th of an inch. Some species have the power of active motion, and may be seen moving rapidly to and fro in the liquid in which they are growing. This motion is produced by flagella, which protrude from the body. Marvelous Multiplication. They mul- Each tiply by simple division or fission. ion. and then divides in individual elongates ates the middle into similar halves; each of which then repeats the process. species the individuals With some remain attached after division, forming preparation. Some 50 years ago it was long chains; others produce solid groups of fours, eights, or sixteens. Some species that have been carefully watched under the microscope have been found, under favorable conditions, to grow so rapidly as to divide every half hour. At this rate in one day each microbe would produce over 16,000,000 descendants. At the end of the third day they would number millions of millions, the bulk and weight of which would be enormous, were it not that their rate of multiplication is checked either by lack of food or by the accumulation of their own excreted products, which are injurious to them. Harmful Bacteria. - Bacteria abound in all putrescent or fermenting mixtures organic matter, and are the containing ng cause of fermentation and putrefaction. Some are present in, and the cause of, or ferment certain of the zymotic diseases, such as malignant pustule, erysipelas, tuberculosis, etc. Micrococci are spheroidal bacteria, and very small, never more than 1-25000th of an inch in diameter, often less. If they are kept out of surgical wounds, there is no suppuration. The discovery of this fact made hundreds of operations possible which of old were thought to be out of the reach of art-hence the wonderful success of antiseptic surgery. Bacillus Tuberculosis. - Very great interest attaches to the bacillus tuberculosis, which is so constantly present that it is used as a means of differentiating the inflammatory diseases of the lungs from tuberculosis. This organism always produces the disease when oculated into animals. Statistics have been published showing that the bacillus was present in 2,417 out of 2,509 cases of supposed tuberculosis. Useful Bacteria. -In many respects bacteria are man's greatest benefactors; for upon their activities is founded the continued life of the animal and vegetable kingdoms. As microbes consume the material which serves them as food they produce chemical changes therein, resulting in simpler products called cleavage products. decomposition or Sometimes, however, they possess the power of building other compounds out fragments, ts, thus building up as well of fr as tearing down. There are various industries based upon the decomposition powers of bacteria-viz., the maceration industries in the separation of the valuable fibers from the useless fibrous material in the preparation of linen, jute, hemp, and cocoanut fiber; also in the commercial preparation of sponges, and often in the early stages of leather found that the mysterious substance known to brewers as yeast or barm was really composed of a vast number of minute oval particles that are endowed with the powers of growth and multiplication, and, therefore, undoubtedly living. Bacteria in the Dairy. In the majority of butter-making countries the cream is subjected to a process known as ripening or souring before it is churned; the cream is allowed to stand for from 12 to 17 hours, thus giving the bacteria an opportunity to grow in it. As a result the cream becomes somewhat soured, slightly curdled. Then the cream is churned. Not only does the ripened cream churn more rapidly and give a larger yield of butter than the sweet cream, but there are developed the peculiar flavor and aroma which are characteristic of the highest product. The dairymen in the great butter producing countries of northern Europe are making practical use of this knowledge and are utilizing pure cultures of certain bacteria which have for the been found to be advantageous ous purpose of cream ripening and the production of agreeable flavors. Nitrifying Bacteria. - Everywhere in fertile soil is a class of bacteria which has received the name of nitrifying bacteria. They feed on the soil ingredients and have the same effect on the simple nitrogen cleavage products the vinegarproducing species have on alcohol-viz., bringing about a union with oxygen. Thus these nitrifying organisms form the last link in the chain that binds the animal kingdom to the vegetable kingdom. For the nitrates are left in the soil, and may now be seized upon by the roots of plants and begin once more the journey around the food cycle. In this way it will be seen that while plants, by building up compounds, form the connecting link between the soil and animal life, bacteria in the other half of the cycle, by reducing them again, give us the connecting link between animal life and the soil. The food cycle would be as incomplete without the agency of bacterial life as it would be without the agency of plant life. Aids to Digestion. The attention of investigators has been directed in modern times to a hitherto unknown class of bacteria which have a share in the process of digestion in the stomach of man and the animals. It has long been known that the mouth, throat, intestines and other organs of the human systern were inhabited by harmless bacteria. It was announced by Vignal that certain other microbes found habitually in the stomach possess properties similar to that of the saliva in aiding digestion. Numerous specimens were obtained and pure cultures made. With the artificially bred microbes a lot of experiments were tried. At least two kinds of organism were distinguished. One promoted the digestion of starch and another that of meat and albuminous substances. One acted most efficiently when it was slightly acidulated. The other needed to be a little alkaline. A third species seemed to have a special fitness for promoting the action of bile on fats.